Add support for generating a StackId when rendering a template

README.md

@@ -169,8 +169,8 @@ The default values for pseudo parameters:
 | **NoValue**      | ""              |
 | **Partition**    | "aws"           |
 | Region           | "us-east-1"     |
-| **StackId**      | ""              |
-| **StackName**    | ""              |
+| StackId          | (generated based on other values)              |
+| StackName    | "my-cloud-radar-stack"              |
 | **URLSuffix**    | "amazonaws.com" |
 _Note: Bold variables are not fully implemented yet see the [Roadmap](#roadmap)_
 
@@ -307,7 +307,6 @@ A real functional testing example using Pytest can be seen [here](./tests/test_c
 ### Unit
 - Add full functionality to pseudo variables.
   * Variables like `Partition`, `URLSuffix` should change if the region changes.
-  * Variables like `StackName` and `StackId` should have a better default than ""
 - Handle References to resources that shouldn't exist.
   * It's currently possible that a `!Ref` to a Resource stays in the final template even if that resource is later removed because of a conditional.
 

src/cloud_radar/cf/unit/_template.py

@@ -2,6 +2,7 @@
 
 import json
 import re
+import uuid
 from pathlib import Path
 from typing import Any, Callable, Dict, Generator, List, Optional, Tuple, Union
 
@@ -26,8 +27,8 @@ class Template:
     NoValue: str = ""  # Not yet implemented
     Partition: str = "aws"  # Other regions not implemented
     Region: str = "us-east-1"
-    StackId: str = ""  # Not yet implemented
-    StackName: str = ""  # Not yet implemented
+    StackId: str = ""  # If left blank this will be generated
+    StackName: str = "my-cloud-radar-stack"
     URLSuffix: str = "amazonaws.com"  # Other regions not implemented
 
     def __init__(
@@ -310,6 +311,19 @@ def remove_condtional_resources(self, template: Dict[str, Any]) -> Dict[str, Any
 
         return template
 
+    # If the StackId variable is not set, generate a value for it
+    def _get_populated_stack_id(self) -> str:
+        if not Template.StackId:
+            # Not explicitly set, generate a value
+            unique_uuid = uuid.uuid4()
+
+            return (
+                f"arn:{Template.Partition}:cloudformation:{self.Region}:"
+                f"{Template.AccountId}:stack/{Template.StackName}/{unique_uuid}"
+            )
+
+        return Template.StackId
+
     def create_stack(
         self,
         params: Optional[Dict[str, str]] = None,
@@ -318,6 +332,7 @@ def create_stack(
     ):
         if region:
             self.Region = region
+        self.StackId = self._get_populated_stack_id()
 
         self.render(params, parameters_file=parameters_file)
 

tests/templates/test_stackid.yaml

@@ -0,0 +1,16 @@
+AWSTemplateFormatVersion: 2010-09-09
+Description: "Creates an S3 bucket to store logs."
+
+Resources:
+  UniqueBucket:
+    Type: AWS::S3::Bucket
+    Properties:
+      BucketName: !Sub
+          - 'my-test-${stack_region}-${uniqifier}-bucket'
+          - # AWS::StackId has this format
+            # arn:aws:cloudformation:us-west-2:123456789012:stack/teststack/51af3dc0-da77-11e4-872e-1234567db123
+            # Trying to capture the last piece after the '-'
+            # As stack name could contain "-"s, split on the "/"s first
+            uniqifier: !Select [ 4, !Split [ "-",  !Select [ 2, !Split [ "/", !Ref AWS::StackId ] ] ] ]
+            # Usually you would refer to AWS:::Region, but trying to test StackId creation works as expected
+            stack_region: !Select [ 3, !Split [":", !Ref AWS::StackId]]

tests/test_cf/test_unit/test_stack_stackid.py

@@ -0,0 +1,73 @@
+# Test case that verifies that generation of the value for AWS::StackId works as expected
+
+from pathlib import Path
+
+import pytest
+
+from cloud_radar.cf.unit._template import Template
+
+
+@pytest.fixture
+def template():
+    template_path = Path(__file__).parent / "../../templates/test_stackid.yaml"
+
+    return Template.from_yaml(template_path.resolve(), {})
+
+
+def test_function_populated_var(template):
+    expected_value = "arn:aws:cloudformation:us-west-2:123456789012:stack/teststack/51af3dc0-da77-11e4-872e-1234567db123"
+    Template.StackId = expected_value
+
+    actual_value = template._get_populated_stack_id()
+    assert actual_value == expected_value
+
+
+def test_function_blank_var(template):
+    Template.StackId = ""
+
+    actual_value = template._get_populated_stack_id()
+    # Check all except the UUID
+    assert actual_value.startswith(
+        f"arn:{Template.Partition}:cloudformation:{Template.Region}:{Template.AccountId}:stack/{Template.StackName}/"
+    )
+
+    # Check the UUID part looks UUID like
+    unique_uuid = actual_value.split("/")[2]
+    assert 5 == len(unique_uuid.split("-"))
+
+
+def test_template_blank_var_stack_region(template):
+    Template.StackId = ""
+
+    stack = template.create_stack({}, region="eu-west-1")
+
+    bucket = stack.get_resource("UniqueBucket")
+    bucket_name = bucket.get_property_value("BucketName")
+
+    assert len(bucket_name) == 37
+    assert bucket_name[:18] == "my-test-eu-west-1-"
+    assert bucket_name[30:] == "-bucket"
+
+
+def test_template_blank_var_global_region(template):
+    Template.StackId = ""
+
+    stack = template.create_stack({})
+
+    bucket = stack.get_resource("UniqueBucket")
+    bucket_name = bucket.get_property_value("BucketName")
+
+    assert len(bucket_name) == 37
+    assert bucket_name[:18] == "my-test-us-east-1-"
+    assert bucket_name[30:] == "-bucket"
+
+
+def test_template_populated_var(template):
+    Template.StackId = "arn:aws:cloudformation:us-west-2:123456789012:stack/teststack/51af3dc0-da77-11e4-872e-1234567db123"
+
+    stack = template.create_stack({})
+
+    bucket = stack.get_resource("UniqueBucket")
+    bucket_name = bucket.get_property_value("BucketName")
+
+    assert "my-test-us-west-2-1234567db123-bucket" == bucket_name